C20.0046: Database Management Systems Lecture #20 M.P. Johnson Stern School of Business, NYU Spring, 2008 M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Agenda Stored procedures? Triggers Transactions RAID? Implementation? M.P. Johnson, DBMS, Stern/NYU, Spring 2008

Programming: step back Recall basic problem: need SQL plus stronger programming lang  need to connect the two langs In all these cases (and in the web app case), idea is: put SQL in (traditional-lang) programs Another way: put programs in SQL i.e., store programs on the DBMS “stored procedures” M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Next topic: SPs “Persistent, Stored Modules” / “Stored Procedures / “PL/SQL programs” (in Oracle) Another way to connect application programming language and SQL Supports usual things: Declare, set vars to vals of expressions Print output Define (optional) procedures, functions Cursors PL/SQL can compute n! Help perform computations not possible using the SQL query language alone. - For example, you can embed business logic in PSM instead of putting it in the programming language. - The DBA can give authorizations for users to run a PSM but not to modify it – useful to enforce security. - One can perform batch-updates using PSMs – where several tables need to be refreshed in a particular sequence. M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Integration with SQL DECLARE l_book_count INTEGER; BEGIN SELECT COUNT(*) INTO l_book_count FROM books WHERE author LIKE '%FEUERSTEIN, STEVEN%'; DBMS_OUTPUT.PUT_LINE ( 'Steven has written (or co-written) ' || l_book_count || ' books.'); -- Oh, and I changed my name, so... UPDATE books SET author = REPLACE (author, 'STEVEN', 'STEPHEN') END; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 PL/SQL “Procedural Language/SQL” Oracle’s language for stored procedures MySQL’s is similar Simple, interpreted, procedural language But Pascal-like: BEGIN END, not { } AND OR, not && || vars defined at top of procedure how return works M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 PL/SQL Generally speaking can be used wherever SQL can be Sql command-line embeded SQL JDBC/PHP/etc Can store programs in files (.sql), run later CALL myprog.sql runs code in myprog.sql M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 PL/SQL: Hello, World http://pages.stern.nyu.edu/~mjohnson/oracle/plsql/hello.sql BEGIN -- print out message DBMS_OUTPUT.PUT_LINE('Hello World, from PL/SQL'); END; / M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Hello, World Try again… SET SERVEROUTPUT ON BEGIN -- print out message DBMS_OUTPUT.PUT_LINE('Hello World, from PL/SQL'); END; / M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 How to run code The code before ended with a forward slash Not SQL and not PL/SQL – just for SQL*Plus to tell it to run the code entered Must go on its own line O.w., will be ignored and then interpreted as part of code, causing an error To call a procedure in SQL*Plus, can also use execute/exec: exec DBMS_OUTPUT.PUT_LINE('Hello World, from PL/SQL') M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 How to run code EXEC is just short-hand: SQL> exec dbms_output.put_line('hi '); dbms_output.put_line('there' M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 SP operators/symbols ; end statement % attribute indicator (cursor attributes like %ISOPEN and indirect declaration attributes like %ROWTYPE : host variable indicator <> and != not-equal-to = equal-to := assignment op ** exponentiation operator -- , /* and */, rem comments M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Var names identifiers limited to 30 alpha-num chars Must start with letter, $, _, or # E.g.: abc, $a$, $$$ PL/SQL is case INsensitive abc, ABC, AbC all the same Unless you use double-quotes… Also supports constants: Varname datatype CONSTANT := val; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Literals Numbers: 123, 12.3, 3.05E19, 12e-5, null String: 'abc', 'AbC', null String comparison is case-SENSitive Boolean: true, false, null true != ‘true’ No date literals, as in regular SQL To_date('31-JAN-94') Escape single-quotes in strings with two single-quotes 'it''s'  it's ''''''  '' M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Blocks SP languages are block-structured Block = seq. of instructions, with scope Can have anonymous blocks And named blocks Procedures Functions M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Structure of a block header --if named DECLARE --optional --var declarations BEGIN --executable statements --queries/updates, etc. EXCEPTION --optional --catch exceptions END; / --to execute As in Pascal, var declars precede body Declarations – usually variables to be used to store parameters passed from outside, and/or to hold local values M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 PL/SQL code examples One example: Likes(drinker, beverage) Another example: http://pages.stern.nyu.edu/~mjohnson/oracle/plsql/age.sql BEGIN INSERT INTO Likes VALUES(‘Izzy', ‘milk'); DELETE FROM Likes WHERE drinker = ‘Izzy' AND beverage = ‘Beaujolais Nouveau '; COMMIT; END; / M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Procedures Stored database objects that use a PL/SQL statement(s) in their body Create/drop similar to other SQL objects: CREATE PROCEDURE <my-proc> (<params>) AS <procedure body as above>; CREATE OR REPLACE PROCEDURE <my-proc>(<params>) AS <procedure body as above>; DROP PROCEDURE <my-proc>; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Example procedure Define the procedure: Now we can call it: CREATE PROCEDURE testProcedure AS BEGIN INSERT INTO Student VALUES (5, 'Joe'); END; EXEC testProcedure M.P. Johnson, DBMS, Stern/NYU, Spring 2008

More details on procedures Parameter list has name-mode-type triples: Modes: IN, OUT, or IN OUT Fulfills role similar to pass-by-value v. pass-by-reference Default is IN Types must match, so can get exact field type: relation.attribute%TYPE M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Procedure I/O example A procedure to take a beer and price and add it to Joe's menu: Sells(bar, beer, price) CREATE PROCEDURE izzyMenu( b IN char(20), p IN double) AS BEGIN INSERT INTO Sells VALUES('Izzy''s', b, p); END; / Are these the right types? M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Procedure I/O example A procedure to take a beer and price and add it to Joe's menu: Sells(bar, beer, price) CREATE PROCEDURE izzyMenu( b IN Sells.beer%TYPE, p IN Sells.price%TYPE) AS BEGIN INSERT INTO Sells VALUES('Izzy''s', b, p); END; / M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Larger procedure e.g. CREATE or replace PROCEDURE hike_prices(old_price number, new_price out number, percent_hike number := 5) is Begin new_price := old_price + old_price * percent_hike/100; End; / M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Call the procedure Declare currprice number := 20; newprice number; Begin hike_prices(currprice,newprice,5); dbms_output.put_line(newprice); End; But how to use to modify table data? Convert to a function M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Functions Like procedures but with return values Big strength: can be called from SQL itself CREATE FUNCTION <functionName> (<paramList>) RETURN type AS <localDeclarations> BEGIN <functionBody> END; DROP FUNCTION <functionName>; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Function example http://pages.stern.nyu.edu/~mjohnson/oracle/plsql/maxval.sql CREATE OR REPLACE FUNCTION maxval(a IN int, b IN int) RETURN int AS BEGIN IF a > b THEN RETURN a; ELSE RETURN b; END IF; END maxval; INSERT INTO R VALUES('abc', maxval(5,10)); M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Hike function CREATE or replace FUNCTION hike_pricesf(old_price number, percent_hike number := 5) return number is Begin return old_price + old_price * percent_hike/100; End; / Now can use directly in update statements NB: had to use different name for ftn Same namespace for ftns & procs, although different M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 How to run scripts Usually don’t type ftns into sqlplus by hand Define them in a .sql file In sqlplus, execute .sql file Runs commands in file Here, defines function Now, we can call functions (they persist) See http://pages.stern.nyu.edu/~mjohnson/oracle/plsql/plsql.txt SQL> CALL maxval.sql SQL> exec DBMS_OUTPUT.PUT_LINE (maxval(5,10)) M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 ED command Though define procedures at cmd-prompt Forgot AS! Type ED… SQL> create or replace procedure hello2 begin dbms_output.put_line('hi'); end; / M.P. Johnson, DBMS, Stern/NYU, Spring 2008

Calling functions and procedures Procedures can executed, ftns can’t How to just call a ftn? Can use dbms_output, as seen Can also select the ftn value from dual SQL> select(wordcount('hi there') from mytable; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

Stored ftns & procs persist Once a function or procedure is created, it persists until it’s dropped Stored procs are stored in the DB itself In user_procedures in Oracle Also, can describe ftns and procs: CREATE OR REPLACE FUNCTION … SELECT object_name from user_procedures; SQL> describe wordcount M.P. Johnson, DBMS, Stern/NYU, Spring 2008

Look up procedures, functions In Oracle, functions & procedures in user_procedures: Also, can describe ftns and procs: SELECT object_name from user_procedures; SQL> describe wordcount M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Getting errors Simply says: To get actual errors, say SHOW ERR(ORS) Can also get errors per object: Warning: must get object type right! Can also look at user_errors tbl directly Warning: Function created with compilation errors. SQL> show errors function wordcount M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Branching IF–THEN statements use THEN Must end with END IF Use ELSIF in place of ELSE IF Example: http://pages.stern.nyu.edu/~mjohnson/dbms/eg/lec19/maxval.sql IF <condition> THEN <statement(s)> ELSIF END IF; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

Simple case statements CASE expression WHEN result1 THEN statements1 WHEN result2 THEN statements2 ... ELSE statements_else END CASE; General form: ELSE is optional expression and results are scalars numbers, chars, strings, etc.; not tables Literals or vars M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Simple case e.g. CASE employee_type WHEN 'S' THEN award_salary_bonus(employee_id); WHEN 'H' THEN award_hourly_bonus(employee_id); WHEN 'C' THEN award_commissioned_bonus(employee_id); ELSE RAISE invalid_employee_type; END CASE; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 CASE statements in SQL By the way: CASE statements are now supported in Oracle SQL itself SELECT CASE WHEN comm is null THEN 0 ELSE comm END FROM emp; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Loop example DECLARE     i NUMBER := 1; BEGIN     LOOP         INSERT INTO T1VALUES(i,i); i := i+1;         EXIT WHEN i>100;     END LOOP; END; / M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 More loops Numerical for loop: Cursor for loop: FOR for_index IN low_value .. high_value LOOP executable_statements; END LOOP; FOR record_index IN my_cursor LOOP executable_statements; END LOOP; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 http://pages.stern.nyu.edu/~mjohnson/oracle/plsql/wordcount.sql Word count program CREATE OR REPLACE FUNCTION wordcount (str IN VARCHAR2) RETURN PLS_INTEGER AS /* words PLS_INTEGER := 0; ***Commented out for intentional error*** */ len PLS_INTEGER := NVL(LENGTH(str),0); inside_a_word BOOLEAN; BEGIN FOR i IN 1..len + 1 LOOP IF ASCII(SUBSTR(str, i, 1)) < 33 OR i > len THEN IF inside_a_word words := words + 1; inside_a_word := FALSE; END IF; ELSE inside_a_word := TRUE; END LOOP; RETURN words; END; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

Explicit cursors v. for loop cursors DECLARE CURSOR occupancy_cur IS SELECT pet_id, room_number FROM occupancy WHERE occupied_dt = TRUNC (SYSDATE); occupancy_rec occupancy_cur%ROWTYPE; BEGIN OPEN occupancy_cur; LOOP FETCH occupancy_cur INTO occupancy_rec; EXIT WHEN occupancy_cur%NOTFOUND; update_bill (occupancy_rec.pet_id, occupancy_rec.room_number); END LOOP; CLOSE occupancy_cur; END; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

Explicit cursors v. for loop cursors DECLARE CURSOR occupancy_cur IS SELECT pet_id, room_number FROM occupancy WHERE occupied_dt = TRUNC (SYSDATE); BEGIN FOR occupancy_rec IN occupancy_cur LOOP update_bill (occupancy_rec.pet_id, occupancy_rec.room_number); END LOOP; END; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

Using query results: SELECT … INTO create or replace function getprod(manuf varchar) return varchar as pn varchar(255); begin select prodname into pn from products where mfg = manuf; return pn; end; / M.P. Johnson, DBMS, Stern/NYU, Spring 2008

SELECT … INTO and exceptions create or replace function getprod(manuf varchar) return varchar as pn varchar(255); begin select prodname into pn from products where mfg = manuf; return pn; Exception When TOO_MANY_ROWS then dbms_output.put_line('got too many'); end; / M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Programs and rights By default, only the creator of a program may run it (apart from the admin) If others should run, must GRANT them permission: Permissions can be revoked: Can also grant to particular roles or everyone: Wider/narrower grant ops are independent… SQL> GRANT EXECUTE ON wordcount TO george; SQL> REVOKE EXECUTE FROM wordcount TO george; SQL> GRANT EXECUTE ON wordcount TO dba_role; SQL> GRANT EXECUTE ON wordcount TO public; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Packages Functions and procedures (and vars) can be grouped in packages Like Java packages, C++ namespaces, etc. A pkg has a specification and a body Somewhat like C++ class definitions Specification: declares public functions “public” means: can be run by a user with EXECUTE authority on this pkg Body: defines all functions Vars defined here are visible to the pkg’s programs M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Dynamic PL/SQL Saw “dynamic SQL” in the cases of Pro*C and JDBC Ability to run ad-hoc (non-hard-coded) SQL in programs/scripts Can also do this in PL/SQL The string can be passed in, created from concatenation, etc. EXECUTE IMMEDIATE <string>; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Dynamic PL/SQL E.g.: write function to return number rows in an arbitrary table CREATE OR REPLACE FUNCTION rowCount ( tabname IN VARCHAR2) return integer as retval integer; begin execute immediate 'select count(*) from ' || tabname into retval; return retval; end; / M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Dynamic PL/SQL for DDL Ordinarily can’t do DDL in PL/SQL But you can in dynamic PL/SQL Here’s an e.g.: CREATE OR REPLACE procedure dropproc(procname in varchar2) as begin execute immediate 'drop procedure ' || procname; end; / M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Live examples Factorial function: http://pages.stern.nyu.edu/~mjohnson/dbms/plsql/fact.sql Converting between bases: http://pages.stern.nyu.edu/~mjohnson/dbms/plsql/numsys.sql Directory of examples: http://pages.stern.nyu.edu/~mjohnson/dbms/plsql/ M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 SPs in MySQL (5.0) Generally similar, though technical diffs Need to temporarily redefine ; delimiter mysql> drop procedure if exists hello; myslq> delimiter / mysql> create procedure hello() -> begin -> select 'hi'; -> end; -> / mysql> delimiter ; mysql> call hello(); M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 New topic: Triggers PL/SQL programs that run automatically (are “triggered”) when a certain event occurs E.g.: on insert to some table On system start-up On delete from table Big benefit: need not be called explicitly However row in table x is deleted, the trigger gets called M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Trigger events Trigger code may be “triggered” by many kinds of events: Oracle start-up/shut-down Triggers may replace initialization scripts Data updates: Delete: maybe delete related rows Inserts Updates: maybe make other rows consistent Delete: maybe prevent DDL statements Log creation of all objects, e.g. M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Triggers Constraints state what must remain true DBMS decides when to check Triggers are instructions to perform at explicitly specified times Three aspects: An event (e.g., update to an attribute) A condition (e.g., a test of that update value) An action (the trigger’s effect) (deletion, update, insertion) When the event occurs, DBMS checks the constraint, and if it is satisfied, performs the action M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 DML trigger options The trigger may be: Statement-level (e.g., a DELETE WHERE statement) or Row-level (e.g., for each row deleted) The trigger may run BEFORE AFTER or INSTEAD OF the statement (in Oracle, not in others) It may be triggered by INSERTs UPDATEs DELETEs M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Trigger form CREATE [OR REPLACE] TRIGGER trigger name {BEFORE | AFTER | INSTEAD OF} {INSERT | DELETE | UPDATE | UPDATE OF column list} ON table name [FOR EACH ROW] [WHEN (...)] [DECLARE ... ] BEGIN ... executable statements ... [EXCEPTION ... ] END [trigger name]; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Trigger type examples First run copy_tables.sql statement_vs_row.sql INSERT INTO to_table SELECT * FROM from_table; before_vs_after.sql one_trigger_per_type.sql INSERT INTO to_table VALUES (1); UPDATE to_table SET col1 = 10; DELETE to_table; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 DML Trigger e.g. CREATE OR REPLACE TRIGGER validate_employee_changes BEFORE INSERT OR UPDATE ON employee FOR EACH ROW BEGIN check_age (:NEW.date_of_birth); check_resume (:NEW.resume); END; Q: Why is this (maybe) better than client-side validation? M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Triggers with WHEN CREATE OR REPLACE TRIGGER check_raise AFTER UPDATE OF salary, commission ON employee FOR EACH ROW WHEN ((OLD.salary != NEW.salary OR (OLD.salary IS NULL AND NEW.salary IS NULL)) OR (OLD.commission != NEW.commission OR (OLD.commission IS NULL AND NEW.commission IS NULL))) BEGIN ... END; NB: WHEN applies only to row-level triggers M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Triggers with WHEN Parentheses are required Can only call built-in functions in when Packages like DBMS_OUTPUT are not allowed CREATE OR REPLACE TRIGGER valid_when_clause BEFORE INSERT ON frame FOR EACH ROW WHEN ( TO_CHAR(SYSDATE,'HH24') BETWEEN 9 AND 17 ) ... M.P. Johnson, DBMS, Stern/NYU, Spring 2008

Simple trigger example R(id, data, last-modified) data is a large string Last-modified is a newly added date field Goal: whenever data is modified, update last-modified date Could modify all scripts/programs that touch this table Bad idea Better: user a trigger CREATE TRIGGER UpdateDateTrigger AFTER UPDATE OF data ON R REFERENCING NEW ROW AS NewTuple FOR EACH ROW BEGIN NewTuple.last-modified = sysdate; END; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Multiple DML actions DML actions may be ORed together CREATE OR REPLACE TRIGGER three_for_the_price_of_one BEFORE DELETE OR INSERT OR UPDATE ON account_transaction FOR EACH ROW BEGIN IF INSERTING THEN :NEW.created_by := USER; :NEW.created_date := SYSDATE; ELSIF DELETING audit_deletion(USER,SYSDATE); END; To find actual action, check: INSERTING DELETING UPDATING M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 More on UPDATING UPDATING may be called for partic. columns CREATE OR REPLACE TRIGGER validate_update BEFORE UPDATE ON account_transaction FOR EACH ROW BEGIN IF UPDATING ('ACCOUNT_NO') THEN errpkg.raise('Account number cannot be updated'); END IF; END; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

Extended auditing example Tables: grades, grades_audit Run: grades_tables.sql, grades_audit.sql Cases: hacker changes grades, deletes others UPDATE grades SET grade = 'A+' WHERE student_id = 1 AND class_id = 101; DELETE grades WHERE student_id = 2 AND class_id = 101; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

Extended auditing example Run: grades_tables.sql, grades_audit2.sql Cases: hacker changes student or class ids UPDATE grades SET student_id = 3 WHERE student_id = 1 AND class_id = 101; UPDATE grades SET student_id = 1 WHERE student_id = 2 AND class_id = 101; UPDATE grades SET student_id = 2 WHERE student_id = 3 AND class_id = 101; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 DDL Triggers Respond to DDL events Creating/dropping tables, indices, etc. ALTER TABLE etc. General form: CREATE [OR REPLACE] TRIGGER trigger name {BEFORE | AFTER| {DDL event} ON {DATABASE | SCHEMA} DECLARE Variable declarations BEGIN ... some code... END; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 DDL trigger e.g. Town crier examples triggered by creates: uninformed_town_crier.sql informed_town_crier.sql M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Available DDL events CREATE, ALTER, DROP, GRANT, RENAME, REVOKE, TRUNCATE DDL: any DDL event Q: Does this work?? CREATE OR REPLACE TRIGGER no_create AFTER CREATE ON SCHEMA BEGIN RAISE_APPLICATION_ERROR (-20000, 'ERROR : Objects cannot be created in the production database.'); END; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 DB Event triggers Form similar to DDL triggers: Triggering events: STARTUP, SHUTDOWN, SERVERERROR, LOGON, LOGOFF CREATE [OR REPLACE] TRIGGER trigger name {BEFORE | AFTER} {database event} ON {DATABASE | SCHEMA} DECLARE Variable declarations BEGIN ... some code... END; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 DB event restrictions Have BEFORE and AFTER as above, but they don’t always apply: No BEFORE STARTUP/LOGON/SERVERERROR No AFTER SHUTDOWN/LOGOFF M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 DB Trigger e.g. Gather stats before shutdown: Log error messages CREATE OR REPLACE TRIGGER on_shutdown BEFORE SHUTDOWN ON DATABASE BEGIN gather_system_stats; END; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

New-old topic: Transactions So far, have simply issued commands Ignored xacts Recall, though: an xact is an operation/set of ops executed atomically In one instant ACID test: Xacts are atomic Each xact (not each statement) must leave the DB consistent M.P. Johnson, DBMS, Stern/NYU, Spring 2008

Default xact behavior (in Oracle) An xact begins upon login By default, xact lasts until logoff Except for DDL statements They automatically commit Examples with two views of tbl… But with TYPE=innodb ! mysql> set autocommit = 0 M.P. Johnson, DBMS, Stern/NYU, Spring 2008

Direct xact instructions At any point, may explicitly COMMIT: SQL> COMMIT; Saves all statements entered up to now Begins new xact Conversely, can ROLLBACK SQL> ROLLBACK; Cancels all statements entered since start of xact Example: delete from emp; or delete junk; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

Direct xact instructions Remember, DDL statements are auto-committed  They cannot be rollbacked Examples: Q: Why doesn’t rollback “work”? drop table junk; rollback; truncate table junk; rollback; M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Savepoints Xacts are atomic Can rollback to beginning of current xact But might want to rollback only part way Make 10 changes, make one bad change Want to: roll back to before last change Don’t have Word-like multiple undo But do have savepoints M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 Savepoints Create a savepoint: emp example: SAVEPOINT savept_name; --changes SAVEPOINT sp1; SAVEPOINT sp2; SAVEPOINT sp3 ROLLBACK TO SAVEPOINT sp2; ROLLBACK TO SAVEPOINT sp1; Can skip savepoints But can ROLLBACK only backwards Can ROLLBACK only to last COMMIT M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 AUTOCOMMIT Finally, can turn AUTOCOMMIT on: Oralce: SQL> SET AUTOCOMMIT ON; Mysql: mysql> SET AUTOCOMMIT=1; Can put this in your config file Can specify through JDBC, etc. Then each statement is auto-committed as its own xact Not just DDL statements M.P. Johnson, DBMS, Stern/NYU, Spring 2008

M.P. Johnson, DBMS, Stern/NYU, Spring 2008 RAID levels RAID level 1: each disk gets a mirror RAID level 4: one disk is xor of all others Each bit is sum mod 2 of corresponding bits E.g.: Disk 1: 10110011 Disk 2: 10101010 Disk 3: 00111000 Disk 4: How to recover? What’s the disadvantage of R4? Various other RAID levels in text… M.P. Johnson, DBMS, Stern/NYU, Spring 2008